Drafting instrument



Sept. 16, 1941-. J. McK. BALLOU I DRAFTING INSTRUMENT Filed March 11, 1941 FIG FIQ. 5

MK MN INVENTOR.

Patented Sept. 16, 1941 UNITED STATES PATENT OFFICE John McK. Ballou, Les Angeles, Califl, assignor to S. M. Tymannw and Leo Schinagel, doing business as Advance Aircraft Tool Company, Los

Angeles', Calif;

Application March' 1-1, 1941, Serial No. 382,767

4 Claims. (Cl. 33--30) This invention relates to drafting instruments in general, and more particularly to an instrument for drawing any ellipse of which. the major and the minor axes, and the major and the minor diameters are known.

I am aware that others have made instruments for generating ellipses, many of which are excellent devices. However, they are all limited by inconvenience to the draftsman', high cost of manufacture, or inability to cover a sufii'ciently wide range of sizes of ellipses, to be fully practical.

It is an object of this invention to provide an ellipsograph of convenient form for a draftsman to use.

It is a further object to provide an. ellipsoigraph adaptable to inexpensive manufacture.

It is a further object to provide an ellipsograph wherein adjustment to generate any ellipse whose major and minor axes, and whose major and minor diameters are known, can be made inv a definite manner.

' Further objects will appear from consideration of the ensuing specification and claims, and a survey of the annexed drawing, wherein a pre'- ferred embodiment of this invention is described in detail. Referring to the drawing:

Fig. l is a plan view of an embodiment of this invention.

Fig. 2 is a front elevation of the embodiment shown in Fig. 1.

Fig. 3 is a cross section taken on: reference plane AA, to a somewhat enlarged scale.

Fig. 4 is a fragmentary longitudinal section, showing in greater detail, and to a somewhat en-- larged scale, the construction of an element of Fig. 1, and

Fig. 5 is a cross section, to a somewhat enlarged scale taken on reference plane B-B.

A main frame I, formed of sheet metal or any other suitable material, is adapted to support a left hand rack 2, and a right handrack 3. Rack 2 is provided with teeth 4, and rack with teeth 5. A blank 6 and a blank I are provided at the extremities of racks 2 and 3 respectively; to serve as stops, preventing the inadvertent losing of racks 2 and 3 by over-adjustment. A thumb wheel 3 is spun-riveted or otherwise suitably secured in a rigid manner tothe outside extremity of spindle 9, whose other end is integralwith, or tightly secured to toothedpinion H1. The teeth of pinion l0 mesh simultaneously with the teeth of racks 2 and 3, so that turning wheel 1% results in equal co-ordinated movements inopposite directions, parallel to the longitudinal axis pivot H, fashioned on spindle 9, and co-axial therewith, protrudes thru a hole in main frame I-, for free, guided rotation of spindle 9, and therewith of pinion ID.

A clip l2, positioned centrally on frame I is secured thereto by lugs l3, bent tightly into con tact with the lower face thereof, or if desired, by electric spot welding thereto, and a holethru the center of clip 12 admits spindle 9,. and, co-acting with the hole for" pivot H, rotationally supports and guides spindle 9'.

An. arm [A is secured by electric spot welding, riveting, or other suitable means to the right hand extremity of right hand rack 3. This arm M is shown more in detail in Fig. 5, and isformed to such a contour, and of such proportions that it misses contact with main frame 1, or any part thereof thus allowing: of its free motion right and left, when rack 3 is adjusted by means of wheel 8, yet, its upper portion 15', when in use, lies close to the plane of the paper upon which an ellipse is being: drawn by the aid of the subject of this invention. This upper portion I5 terminates in an edge I'Blying in astraight line parallel to the" longitudinal axisof the device, and therefore, parallel to the motion of adjustment of rack 3. A lug I1 is formed at the left hand ex-- tremity of edge l6, containing an eye' l8 whose center is on a continuation of the line of edge [6.

Similarly, another arm I9 is secured to the left hand extremity of left hand rack 2, pro-- vided with an upper portion 20, terminating in of' the instrument, of racks 2 and 3-. Aguide an: edge 21, lying on the same straight line as edge l6 of armi4, with lug 22 and eye 23centrall y' located on this line and at the right hand end of edge 21-.

A funi'cle 24-, of suitable material, such as for example, fine braided fishing line, is secured in.

eye I8 by a knot 25; and passes down thru eye [8, knot 25 preventing it from slipping clear thru. Funicle 24" rises again thru eye 23 thence to pass under thumb nut 26, screwed onto stud 2-1- which isi'mmovably secured to arm 19- at any convenient location, and which, when screwed down tightly, grips funicle 24, securing it against slipping. thru eye 23 when in any adjusted position, ready for use; The free end'of funicle- 24- may be Wrapped around drum 2-8,, which} is centrally located on clip: I2 and secured thereto, as for example, by electric spot welding.

The upper head 29 of drum 28, secured thereto for example by spot welding, is provided with a hole 30 thru which spindle 9-rota-tab1y protrudes. Anyone skilled in the art can understand how drum 28 could as well, if desired, be replaced slides, and, co-acting with the turned back edges 3 I, constrain racks 2 and 3 to longitudinal move ments only, whereby edges l6 and 2|, always lie on the same straight line, regardless of their positions of adjustment. Also, because of both racks;

2 and 3, being meshed with the. same pinion I0, any movement of one rack is necessarily accompanied by an equal and opposite movement of the other. The channel pieces 32 and'33 are secured to main frame I by spot welding, riveting, or

other appropriate fastenings, and the spots 34' can represent either rivets or weld spots, both in the case of the channel pieces 32 and 33, andof the arms l4 and Hluponracks 2 and.3. Likewise, the drum 23 with its head 29 may. equally well be joined by welding, by. bent over tabs thru slots, or by any other means familiar .to those skilled in the art.

r A scale 35 is slidably secured to frame I. Itzis provided with a straight edge 36, and is mounted under frame I so that edge 33 lies on the axisof rotation of spindle 9, and is always perpendicular to the straight line containing edges I6 and 2|. This scale may he graduated to read on either the upper edge 37 or the lower edge 38 of clip I2, according to the preference of the designer of any particular model. Graduations 39 are so placed on scale 35, in either case, that the readings show the distance above the straight line of edges l3 and 2|, of the extremity 43 of scale 35. U

The straight edge portion 36 of scale 35, is preferably bent over as shown in Fig. 4, so that it touches the draftsmans paper when in use. The top of scale 35 may be trimmed on a bias relative to straight edge 33, exposing only the bent down portion of scale 35 at its extremity 4|]. Rivets 42, or, if desired,.bumps, may advantageously be provided on scale 35 near its upperand lower extremities to serve as detents to inhibit the inadvertent loss of scale 35.

Ears 43 are bent down out of the substance of frame I, under racks 2 and 3, with their inner faces lying in a plane passed thru the axis of rotationof .spindle 9, and perpendicular tothe line thru edges l and 2|, as shown in Fig. 4. These serve as guidesfor maintaining straight edge 36 of scale 35 in its correct position, regardless of its. slidable position of adjustment as described above. An alternative construction is shown in Fig. 2, where ears 43 are curved, so that only their lower. edgescontact with straight edge 36. Eitherconstruction serves the samepurpose. More of the material of frame I is formed to a suitable shape to constitute guides 44 for scale 35. Also, the edge 45 of scale 35 opposite straight edge 36 lies in contact with lugs IS on the right hand side. of clip l2, thereby being more completely guided to constrain its motion to a line perpendicular to the line of edges l6 and,2|. Owing to the bumps or rivets 42, it can never be pushed out far enough to be completely.disen-- aged from frame I.

The endsof frame arebent down to form feet 46, of a length allowing the device to lie on the paper upon which an ellipse is to be drawn, with edge 36 of scale 35 barely in contact with the distance from this same point in the envelope to paper, and at the same time with edges Hi and 2| of arms I 4 and I 9 barely missing'contact with the paper, so as not to impede the movement of funicle 24.

The utility of this device depends upon certain well known properties of the ellipse. The distance from a focus to the intersection of the minor axis with the envelope is equal to the semimajor diameter. The sum of the distance from one focus to any point in the envelope and the V the other focus is equal to the major diameter. The major and minor axes are perpendicular to each'other.

. In use, the major and minor axes are located on the paper, drawn to an indefinite length. Scale 35 is set by means of its graduations to the semi-minor diameter. Funicle 24 is pulled out to leave ample slack between eyes I8 and 23. A pair of dividers is set so that the distance between its points is equal to the semi-major diameter. One point is inserted in eye 23, and thumb wheel 8 is turned until the other point of the dividers comes just even with the extremity 40 of scale 35. In the design of the parts of the device, sufficient tightness is allowed thruout so that when an adjustment is made, there is no tendency for the parts to slip, which would cause a loss of adjustment. The instrument is essentially self-locking against any normal pull in use, which would tend to shift racks 2 and 3, yet, by. the mechanical advantage, when turning thumb wheel 8, the tightness is insuflicient to render adjustment diflicult. When the racks have been moved until the distance between scale extremity 40 and eye 23 coincides with the distance set in the dividers, they are removed. Now, thumb screw 26 is loosened, and funicle 24 is laid over the end of scale 35, and

pulled tight so that it contacts extremity 40, as

is shown in Fig. 1. Thumb screw 26 is tightened again, fixing the effective length of funicle 24, the free end thereof being taken up on drum 28, if desired. Scale 35 is next slid down until its extremity 40 no longer contacts funicle 24. The device is then laid on the paper, with straight edge 36 superposed over the minor axis and edges l6 and 2| superposed over the major axis. This centers the instrument at the location where the desired ellipse is to be drawn. It also locates eyes l8 and. 23 at the two foci of the desired ellipse. A pencil is held against the inside of funicle '24, and the envelope of the ellipse is drawn from major axis, thru one semi-minor axis point, and back to the major axis, which would constitute a half-ellipse. The instrument is now reversed, without making any alterations in the adjustments of its parts, and the other half is drawn, which completes the desired ellipse.

It is manifest that numerous variations in detail could be made by those skilled in the art, and yet accomplish the same results as the specific constructions shown and described hereinbefore. Therefore, the spirit rather than any specific details of construction as shown should be construed as constituting the present invention.

-- Having described my invention, I claim:

1.'In apparatus of the character described, a frame, a'clip centrally secured to said frame, said clip being provided with a plurality of fastening ears engaging the underside of said frame, a pinion and spindle rotatably mounted between said clip and the upper side of said frame, lugs bent downfrom the underside of said frame with faces lying in a transverse plane thru the axis of said spindle, retaining tongues formed from the frame material on its underside, and a measuring scale with parallel edges slidably retained on the underside of said frame by contact with two of said ears and said lugs and said tongues, said scale being provided with limit stops to prevent its removal from said frame.

2. In apparatus of the character described, a frame, a funicle, longitudinally oppositely co-adjustable members slidable in said frame, sheet metal lugs secured to said members with outer portions bent down and terminating in longitudinal co-rectilinear edges, the under surfaces of said portions lying in a plane located below the under surface of said frame, engaging means on said lugs for said funicle on inwardly extending terminations of said portions, said means aligned with said straight edges, a scale laterally slidable under said frame with a straight edge extending laterally thru the central axis of said frame, engaging means for said scale depending downwardly from the under side of said frame near its central axis for constraining said scale to lateral movements of adjustment, and supporting means for the apparatus depending downwardly from the underside of said frame near its longitudinal extremities with terminations lying in a plane located no higher than the lowermost elements of said scale, said scale-engaging means, and said lugs.

3. In apparatus of the character described, a funicle, a frame, co-adjustably positioned engaging means associated with said frame for securing measured segments of said funicle, a clip secured to said frame having its central axis coincident with the central axis of said frame, a coadjusting rotative device operating said engaging means, a drum on said clip for receiving the excess of said funicle, said drum, said clip, and said frame having circular apertures with their axes in perpendicular alignment relative to said frame co-acting to align said device and to constrain it to rotative movements with its axis always coincident with the axes of said apertures.

4. In apparatus of the character described, a frame, longitudinally adjustable members slidable in said frame, the longitudinally extending extreme portions of said frame folded upwardly and inwardly to form tracks for said members, a clip centrally located on said frame positioned by contact with said extreme portions and the underside of the frame, an adjustable scale associated with and sub-imposed under said frame, a surface depending from the underside of said frame lying in a plane thru the vertical axis of said frame and said clip, retaining means depending from the underside of said frame co-acting with said surface to constrain and limit said scale to lateral movements of adjustment with an edge of said scale lying always in said plane thru said axis, and a device associated with said clip, said frame, and said members for co-adjusting their longitudinal positions relative to said frame.

JOHN MCK. BALLOU. 

